1. Field of the Invention
The present invention relates to a combined cycle power plant that combines a gas turbine plant and a steam turbine plant.
2. Description of the Related Art
A combined cycle power plant is a power generation system that combines a gas turbine plant and a steam turbine plant, and heat energy in the high temperature region is allotted to the gas turbine and heat energy in the low temperature region is allotted to the steam turbine. Heat energy is efficiently recovered and used, and recently, in particular, this power generation system has received much attention.
In this combined cycle power plant, research and development is advancing concerning the one point related to increasing efficiency, that is, how high the high temperature region of the gas turbine can be raised.
In contrast, in the formation of the high temperature region, it is necessary to provide a cooling system to maintain the heat resistance of the turbine structure body, and conventionally air has been used as the cooling medium in this cooling system.
However, to the extent that air is used as the cooling medium, for example, even when the high temperature region can be attained, when considering both the power loss necessary for increasing the air used in cooling to the necessary pressure by the air compressor and the result that the energy of the gas decreases because of the decreasing of the average gas temperature due to the final mixing of air used in the cooling of parts inside the turbine flow passage transited by the high temperature gas, an increase over the present heat efficiencies cannot be expected at this point in time.
In order to solve this problem and implement an increase in efficiency, switching the above a cooling medium in the gas turbine from gas to steam has been proposed.
One example of this is Japanese Unexamined Patent Application, First Publication, No. Hei 05-163960. However, although the invention disclosed in this publication discloses the notion of using steam as a cooling medium in a gas turbine, there remain many problems in the details that must be thought about and solved.
For example, while the gas turbine is stopped, the steam that remains in the steam cooling system must be purged, and in the Japanese Unexamined Patent Application, First Publication, No. Hei 05-163960, a gas turbine is structured as shown in FIG. 2 for this purpose.
That is, while the gas turbine 13 is stopped, immediately before stopping, a supply steam stop valve 55 and a recovery steam stop valve 74 are closed, and the supply of cooling-steam from the cooling steam supply system 51 and the recovery of cooled steam via the steam recovery system 53 is cut off.
On the other hand, by opening the exhaust valve 86, and connecting the steam supply system 52 of the turbine high temperature cooled part 13a to the outside of the system via the drain exhaust system 85, the cooling of the turbine 13 is switched to air cooling by the compressor bleeding via the air supply line 81, and at the same time, the residual steam in the cooling steam supply system 51 and the steam supply system 52 is removed to the outside of the system, and it is possible to prevent draining from occurring during stoppage.
In addition, even if in the worst case draining should occur during stoppage in the cooling steam supply system 51 and the steam supply system 52 of the steam cooling system 50A, when the gas turbine is actuated, the drainage will be moved outside the system.
However, during a normal stoppage of the gas turbine, since the pressure of the compressor discharge air falls in a rather short time, there is the concern that not all residual steam can be completely purged with the air volume after stoppage.
In consideration of this, there are operation means that implement purging by switching from cooling steam to compressor discharged air before the gas turbine stoppage, but generally in these switching cooling air systems, because there are cutoff valves, piping, etc., there is naturally pressure loss, and in places in the high temperature parts are applied, the air pressure in the cooling passage is possibly lower than the combustion gas pressure in the working passage.
It is preferable that while the gas turbine is in operation the internal pressure of the cooling passage of the gas turbine high temperature parts be always maintained at a high pressure over the pressure of the combustion gas in the working passage. In the case that in the actual part there is even a small pinhole, the combustion gas will flow back through this hole, and it is possible that local heating and scorching of the connected pipes, not only the cooling passage, will be caused.
One example is explained with FIG. 3. The steam cooling structure in the combustor 1 of the gas turbine 1 generally a cylindrical thin plate structure forming the contours of the combustor, and on the inside, a plurality of steam passages are disposed. On the outside of the cylinder there is the emitted air from the compressor 2, and on the inside is a high temperature gas combusted by slightly decompressing the emitted air (lowered only by the pressure loss incurred while the air transits the air intake of the combustor).
Now, while the gas turbine 3 is in operation, this combustor cooling steam is maintained at a pressure higher than the combustion gas, and before the gas turbine 3 is stopped, this steam is switched to the emitted air of the compressor 2. Thereby, the initial pressure P1 gradually decreases in the process of the emitted air of the compressor 2 transiting the stop valves and pipes disposed in the switching system 4 introduced into the steam cooling system, and in the cooling passages, falls to a final P2. In contrast, the internal pressure of the combustor 1 is P3, and because there is a slight difference between P1 and P3, the state in which P3 greater than P1 can easily occur.
At this time, if there is a small pinhole in the thin plate structure of the combustor 1, the high temperature combustion gas inside will leak to the cooling passages via this hole, and not only will the thin plate structure in the combustor 1 be damaged, but finally the combustion gas arrives at the pipes connecting this cooling system, and the extent of the damage widens considerably.
Therefore, while the notion of using the emitted air of the compressor 2 to purge the steam during a gas turbine stoppage seems promising at first sight, there is the problem produced by this danger.
In order to solve the above-described problem, it is an object of the present invention to provide a means which, when a gas turbine is stopped, just before the stoppage, steam sufficiently pressurized for cooling is used, and immediately after the stoppage, most of it is self-expelled under its own pressure, and the residual part can be more simply, reliably, and safely purged.
In order to solve the above problems, the present invention provides a combined cycle power plant that is structured so as to combine a gas turbine plant and a steam turbine plant, comprises an exhaust heat recovery boiler for generating steam driving steam turbine by using the exhaust heat from the gas turbine, and a steam cooling system for cooling by steam the high temperature cooled part of this gas turbine and the superheated steam from this steam cooling system is recovered in a steam turbine, wherein a combined cycle power plant provides a means that closes the steam entrance of this steam cooling system immediately after the stoppage of the gas turbine, a means for discharging the residual steam to the atmosphere, and a means for supplying dry air, and the important parts of the steam cooling system necessary for purging the residual steam by the means for closing the steam entrance of the steam cooling system are partitioned into sections, the passage for purging the residual steam by the means that discharges the residual steam to the atmosphere is secured, and by supplying dry air to the element parts of this partitioned steam cooling system, the purging of the residual object gas is completed.
In addition, the present invention provides a combined cycle power plant comprising an air reservoir in which the dry air supply means stores a part of the compressor emitted air during operation and a means for eliminating moisture before storage, and by supplying a part of the compressor emitted air stored during operation in the air reservoir after eliminating moisture to the element, parts of the steam cooling system as dry air, the purging of the residual air is completed.
Furthermore, the present invention provides a combined cycle power generating plant that combines a gas turbine plant and a steam turbine plant, and provides an exhaust heat recovery boiler that generates steam to drive the steam turbine by using the exhaust heat from the gas turbine, and at the same time provides a steam cooling system that cools with steam the high temperature cooled parts of the gas turbine, and the superheated steam from this steam cooling system is recovered in a stream turbine, further providing a combined cycle power plant providing a means for closing the steam entrance of the steam cooling system immediately before the gas turbine stoppage, a means for discharging residual steam to the atmosphere, and a means for supplying N2 gas, and wherein the purging of the residual steam using the N2 gas can be carried out simply, reliably, and completely.